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From: tribble_acn%uta.csnet@csnet-relay.arpa (David Tribble)
Newsgroups: net.lang.c
Subject: /-INFINITY and NaN
Message-ID: <978@brl-tgr.ARPA>
Date: Mon, 23-Dec-85 05:13:18 EST
Article-I.D.: brl-tgr.978
Posted: Mon Dec 23 05:13:18 1985
Date-Received: Wed, 25-Dec-85 03:56:08 EST
Sender: news@brl-tgr.ARPA
Lines: 15

A question was raised as to how to compare a float (or double) to
the ANSI +/-infinity and Not-a-Number values.  One suggestion was to
use a struct; another way (though arguably not elegant) is-
	#define INFINITY	(*(float*)"\177\200\0\0")
	#define NaN		(*(float*)"\177\277\377\377")
(I'm not certain of the bit patterns, however). The idea is to cast a
string, which is coerced into a char*, into a float*, thus interpreting
the string chars as elements of a float data value.
The same idea can be extended to doubles.
(This works on one compiler that I know of, running on an 8086).

While this may not seem elegant, it has the advantage of not requiring
any structure initilizations.

	David R. Tribble	<tribble_acn@uta>